1. There are about 105 males born for every 100 females, but this ratio drops to near balance at the age of maturity, and among 70-year-olds there are twice as many women as men.

　　【译文】每出生一百位女婴就约有一百零五位男婴降生，但到成年，这一比例基本持平，七十多岁的老人里，健在的老年女性的数量是老年男性的二倍。

　　【析句】这个长句比较简单，是由三个简单句由and、but连接，形成简单的并列或转折关系，每个简单句中没有增加句子长度的从句。

　　2. This means that, for the first time, there will be an excess of boys in those crucial years when they are searching for a mate.

　　【译文】这意味着到了男孩寻找伴侣的关键年龄将首次出现男孩过剩。

　　【析句】这是一个很典型的复合长句，首先抓主干，主句是一个简单句This means that...，从句在mean后是宾语从句；主句没有从句，这意味着不必分析“主从”；看“从从”，宾语从句there will be an...years后有一个when引导的时间状语从句。至此，基本的逻辑关系就分析清楚了。

　　3. The grand mediocrity of today -- everyone being the same in survival and number of offspring -- means that natural selection has lost 80% of its power in upper-middle-class India compared to the tribes.

　　【译文】今天这种每个人的生存机会和子女数量都相同的极其显著的平均化，意味着与部落相比，自然选择在印度社会中、上层中已经失去了80%的效力。

　　【析句】句子的主干是The grand mediocrity of today means that...(主句)+the natural selection...(宾语从句)，破折号之间是伴随状语；主句和从句中都没有进一步的从句，因此整句话相对来说不难理解。